Various electromagnetic positioning elements are known, for example pressure control valves for use in electrically controlled gear shift systems (see, for example, German Patent Disclosure Document No. DE-OS 26 58 969). Other types of electromagnetic positioning or force generating elements are known, for example electromagnetic positioning elements which position a body in a predetermined location, against the bias force of a spring.
The transfer characteristics between an electrical parameter or value and the mechanical force or position includes hysteresis, since the magnetizing force--magnetization curve of electromagnetic elements includes hysteresis. FIG. 2 illustrates a portion of a typical B-H curve, in which the abscissa represents a magnetizing current, and the ordinate a resultant output value, for example, force, speed, pressure, a positioning distance or the like. The hysteresis is formed by two portions, namely a friction hysteresis and magnetic hysteresis. Frictional hysteresis and inaccuracies can be overcome, or at least reduced to a tolerable level, by modulating the control current with a low-frequency modulation. The magnetic hysteresis can be reduced by utilizing magnetic material based on pure iron and other high-quality materials. Such materials are expensive and difficult to handle. The presence of hysteresis--regardless of whether it is high or low--makes it more difficult to provide exact proportionality between an electrical parameter and a mechanical value, since the extent or degree of hysteresis varies over the extent of the characteristic curve. Tolerances in manufacture and tolerances within the materials used lead to further variations in hysteresis. The gap between the respective curves defining the hysteresis relationship is not precisely determined, and upon change of an input parameter counter the direction of hysteresis, it is not always possible to obtain an output parameter or output condition which will be precisely proportional to the input parameter and predetermined on a fixed point on the characteristic transfer curve between current and mechanical output value, for example.